Electrodes for electric arc torches



Sept. 3, 1963 J. A. BROWNING ETAL 3,102,949

ELECTRODES FOR ELECTRIC ARC TORCHES .Filed Sept. 5, 1961 IN VEN TOR.

6 #0 R W0 0 m A M BY WW (W United States Patent 3,102,949 ELECTRODES FOR ELECTRIC ARC TORCHES James A. Browning, Hanover, N.H., and Abner 0. Lord,

White River Junction, Vt., assignors to Thermal Dynamics Corporation, a corporation of New Hampshire Filed Sept. 5, 1961., Ser- No. 135,905 3 Claims. (Cl. 219-145) Our invention relates to electric arc torches and relates more particularly to an improved type of electrode for use in such torches. We have developed a cathode electrode area of the anode surface. This is not true of the cathode surface. At the current levels now in use, the cathode arcing spot runs in a molten condition. The area of the spot is much smaller than the area of the anode in operative relationship with the arc.

To resist excessive melting, it is the usual practice to make the cathode of some highly refractory material. Since cooling of the are spot on the cathode is essential, the material used should have as high a heat conductivity as possible. Thoriated tungsten is an excellent cathode material in that it combines a high melting point with good thermal conductivity.

It has been the usual practice to use a rather massive tungsten cylinder as the cathode electrode. Such an electrode is shown as element 11, FIGURE 1 of the Browning application referred to above. Although this arrangement is suflicient for moderate power levels, higher currents tend to cause a spitting of the tungsten. The erosion of the tungsten not only contaminates the plasma efflux but results in a short life for the expensive tungsten element.

The use of higher currents is made possible, in'accordance with our invention, by combining a relatively small piece of tungsten with copper. The tungsten serves as the arcing surface, while the copper provides improved cooling with its high heat conductivity. We provide an electrode in which the expensive tungsten is formed in thin section and brazed, welded, or other wise held to a copper body. 1

It is a principal object of our invention to provide a cathode electrode using a minimum of refractory material and a construction to facilitate cooling of the are spot.

For a better understanding of the invention reference is now made to the drawing, in which FIGURE 1 is a view, in section, of a disc-type cathode which is water cooled; 7

FIGURE 2 is a view of a cathode in which the arcing material is separated from the cooling medium;

FIGURE 3 is .a variation of FIGURE 2 with-a hemispherical arcing element;

FIGURE 4 is .a variation of FIGURE 2;

FIGURES 5 and 6 are variations of FIGURE 1; and

FIGURE 7- is another variation of FIGURE 2.

Referring now more particularly to the drawing, in FIGURE 1 a tungsten cathode disc 11 is attached to a copper tube 12 by means of a brazed joint 13. A tube 14 coaxial with tube 12 supplies water under pressure through passage 15. The water (or other suitable cool-- 3,102,949 Patented Sept. 3, 1963 ing medium) strikes the back faceof the thin tungsten disc 11 at high velocity and then flows out through the annular passage 16. The impinging water cools the tungsten at a point quite close to the arcing spot 17. The are column 18 is positioned by gas, magnetic, or other means to the center of the disc 11, as shown.

The fusion temperature of tungsten is approximately 6,300 degrees F., or even higher. Thus, the molten arcing spot 17 is above that temperature. To assure that joint 13 does not fail, a sufi'icient distance across the disc from its center to its edge must be provided. This geometry has proven very satisfactory and allows for the use of current levels of operation which heretofore have led to excessive spitting and its attendant erosion. Using a gas sheath vortex-flow stabilization as described inthe Browning application, supra, no deleterious effects were evident at 1,000 amperes. The disc in this case was one-half inch in diameter and one-eighth of an inch thick; 1

construction shown in FIGURE 2. Here a tungsten disc I 11 is brazed into a shallow well formed at the end of a tube 21 by a thin integral end wall section 22. Again, joint 13 must be a sufficient distance from the center of disc 11 (the arcing spot) to avoid melting of the joint weld material. During high intensity operation, it is probable that any weld material near the center of disc .11 melts. In practice this does not affect satisfactory operation of the unit so long as a circumferentially continuous infused joint is maintained. The thin wall 22 of highly conductive copper provides eifective cooling (from the back) of the disc 11.

Other geometries within the spirit of our invention are, of course, possible. FIGURE 3 illustrates a hemispherical tungsten electrode design. The cooling of the are spot is somewhat less effective, though the shape of the emitting element 25 may be dictated by other considerations.

Where the refractory material is drilled to provide a back cooling chamber, it is desirable to separate the refractory material from the coolant by a thin wall, as shown in FIGURE 4. Here a hollow tungsten piece 31 is brazed to copper element 32. Preferably, the weld ma terial fills the entire interstice between pieces 31 and 32.

Whereas the embodiments thus far described have employed welded or brazed joints, we have found pressure held electrodes equally effective and, in addition, easily replaceable.

Such electrodes are shown in detail in FIGURES 5,

6, and 7. The pressure in each case holding the refractory material 35, 40 and 45 in place is represented by arrows 37 in each of the three figures. This pressure is supplied by assembling the torch in the manner shown in Browning copending application No. 99,403, filed March 30, 1961 now Patent No. 3,047,709 dated July 31, 1962. A threaded nozzle piece, when tightened, provides the endpressure to securely seat the refractory disc against'the copper tube 36 of FIGURE 5. A tapered seat provides sealing and good electrical contact between disc 45, plate 46 and 0 ring 49 may be securely held against the end of holder 47 by pressure developed when theentire torch is assembled. It should be pointed out here that the discof tungsten will rest, in the complete torch, against a swirl ring or other element insulating it from a nozzle which-customarily serves as an anode in the non-transferred mode of operation.

- disc shaped well at the end of said member, and a disc While we have described preferred embodiments of our invention, other variations within the spirit and scope of the appended claims may occur to persons skilled in this art.

We claim: a

1. An electrode for an electric arc torch comprising a closed tubular member of conducting material, an outer of refractory material nested in said well. i

2. An electrode for an electric arc torch comprising an open tubular member, a shoulder formed at the end of said member and having a groove therein, a disc of refractory material adapted to fit the end of and close said member, and a sealing ring element between said disc and said member. I

3. An electrode for an electric arc torch comprising an open tubular member, a shoulder formed at one end of said member and having a groove therein, a disc of refractory material adapted to fit the end of and close said member, a sealing ring in said groove, and a separate plate between said sealing ring and said disc.

References Cited in the file of this patent UNITED STATES PATENTS Haynes Mar. 16, 1948 

1. AN ELECTRODE FOR AN ELECTRIC ARC TORCH COMPRISING A CLOSED TUBULAR MEMBER OF CONDUCTING MATERIAL, AN OUTER DISC SHAPED WELL AT THE END OF SAID MEMBER, AND A DISC OF REFRACTORY MATERIAL NESTED IN SAID WELL. 